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The Texas ET (Evapotranspiration) Network
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Suggested Maintenance Schedule and Procedures
for Automatic Weather Stations
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Proper maintenance of weather station components is essential
for ensuring accurate data collection and reporting. To ensure data quality,
equipment must be in good operating condition. A suggested maintenance schedule
is provided to help the station manager identify potential problems and prevent
serious damage to weather station sensors and peripheral equipment. Periodic
sensor calibration and performance testing by the manufacturer is necessary for
some components.
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Maintenance Schedule and Procedures
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Sensor
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Interval
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Procedure
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Tower
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6 months
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* Check the tower or tripod for structural damage,
proper alignment, and for level.
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Solar Panel
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3 months
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* Clean glass on the solar panel to remove dust and
debris to improve its efficiency.
* Check sensor leads and cables for cracking,
deterioration, proper routing and strain relief.
* Check solar panel orientation on the tripod to ensure
proper tilt and direction. Solar panel should face south.
* If a problem with the solar panel voltage output is
suspected, check the voltage with a voltmeter between the two leads of
the solar panel. There must be a load connected to the solar panel.
Voltage should range between 11.5 and 14.5 volts. Readings out of this
range may indicate a problem with the solar panel’s voltage regulator.
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External Battery
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3 months
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* Clean battery terminals to remove corrosion on
terminals. Replace terminal connectors if corrosion is severe.
* If a problem with the battery voltage output is
suspected, check the voltage with a voltmeter between the two poles on
the battery. Voltage output should range between 11.5 and 13.5 volts.
Readings out of this range may indicate insufficient recharge from the
solar panel or faulty battery.
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Desiccant
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1 month
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* Check the humidity indicator card located inside the
datalogger enclosure. Change the desiccant packs when the enclosure
relative humidity exceeds 35%. The humidity indicator card should be
changed every 3 years.
* Check for proper sealing around the datalogger
enclosure and wiring access hole to prevent pest entry and internal
condensation.
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Solar Radiation (pyranometer)
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1 month
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* Check the level of the pyranometer using the leveling
bubble located on the pyranometer base plate. Adjust leveling screws as
necessary.
* Remove any dust or debris on the sensor head with a
soft bristle brush or compressed air.
* Check that the drain hole next to the surface of the
sensor is free of debris.
* Check sensor leads for cracking, deterioration, proper
routing, and strain relief.
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2 years
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* Submit sensor to manufacturer for recalibration.
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Temperature/Relative Humidity
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1 month
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* Check the temperature/humidity sensor filter for
contamination or debris. The filter is located within the white
radiation shield.
* Check sensor leads for cracking, deterioration, proper
routing, and strain relief.
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6 months
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* Clean the temperature/humidity sensor with distilled
water.
* Remove dust, webs and other debris from the radiation
shield.
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1 year
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* Submit sensor to manufacturer for recalibration.
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Wind Speed/Direction
(anemometer)
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1 month
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* Do a visual/audio inspection of the anemometer at low
wind speeds. Unusual "humming" or rotation may indicate problems with
the anemometer bearings.
* Check sensor leads for cracking, deterioration, proper
routing, and strain relief.
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1 year
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* Replace the anemometer bearings. (This should be
performed by a trained technician or by the manufacturer.)
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2 years
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* Replace the wind vane potentiometer and bearings.
(This should be performed by a trained technician or by the
manufacturer.)
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Rain Gage
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1 month
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* Check the rain gage for debris on the screen and
funnel.
* Check the throat opening on the rain gage for level.
* Check sensor leads for cracking, deterioration, proper
routing, and strain relief.
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1 year
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* Calibrate the rain gage. (This should be performed by
a trained technician or by the manufacturer.)
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Other
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1 month
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* Mow grass around the weather station to expose sensor
wiring. Be careful not to nick or cut wiring, particularly those from
the buried soil temperature probe and rain gage.
* Check for adjacent structures that may influence
sensor measurements. (I.e., shading of solar radiation sensor due to
nearby trees.)
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MAINTENANCE LOG
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Location Description:
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Owner:
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Page
of
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Date
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Equipment/Sensor
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Ö
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Comments
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Tower/Tripod
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Solar Panel
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External Battery
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Desiccant
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Pyranometer
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Temperature/RH
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Anemometer
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Rain Gage
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Date
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Equipment/Sensor
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Ö
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Comments
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Tower/Tripod
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Solar Panel
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External Battery
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Desiccant
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Pyranometer
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Temperature/RH
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Anemometer
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Rain Gage
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Date
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Equipment/Sensor
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Ö
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Comments
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Tower/Tripod
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Solar Panel
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External Battery
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Desiccant
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Pyranometer
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Temperature/RH
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Anemometer
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Rain Gage
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Date
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Equipment/Sensor
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Ö
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Comments
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Tower/Tripod
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Solar Panel
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External Battery
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Desiccant
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Pyranometer
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Temperature/RH
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Anemometer
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Rain Gage
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Bid Specification and Recommendations for Automated Weather
Stations Used in the TexasET Network and Web Site
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All bids submitted for this weather station should be for
equipment and accessories which meet or exceed the following
specifications. The weather stations should have the appropriate equipment to
monitor and store wind speed, wind direction, air temperature, soil temperature,
relative humidity, solar radiation and precipitation. The weather station should
be accessible via a telephone line and modem for reprogramming, real-time
monitoring and downloading data.
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Equipment
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Specifications
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Tower
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The tower should be tall enough to mount anemometer and
pyranometer 2 meters (or 6.6 feet) above the ground. It should be
supplied with all mountings, cross arms and fittings for all sensors,
data logger and power enclosure, solar panel and leveling stand for the
pyranometer. The tower must be suitable for anchoring to the ground and
must include a lightning arrester, grounding rod and cable.
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Datalogger
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The datalogger should have ample inputs for the
specified number of sensors, such as the Campbell CR1000. All inputs
should be surge protected. Input ranges and resolutions chosen for each
sensor should not degrade reading accuracy. Must contain a serial RS232
communication channel. Memory must be large enough to store 50 days of
weather data.
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Datalogger enclosure
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Enclosure must be sealed and lockable, NEMA 4 rated,
white fiberglass. Minimum dimensions: 12" x 14".
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Power
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Power should be provided by a minimum 12V -4Ahr (or
amperage specified by datalogger) sealed battery mounted within the data
logger enclosure. Wiring harness to solar panel and data logger should
be included.
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Modem
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For telephone communications, a modem should be used
that is compatible with the data logger. The modem should have telephone
surge protection and be provided with inputs from telephone tip and ring
signals.
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Solar Panel
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10 Watt nominal power regulated at 13.7 Volts.
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Cabling
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All necessary cabling and connections should be supplied
for sensor, power, and modem communication connections. A 6 foot RS232
cable should also be supplied with any required isolation components to
connect a computer directly to the data logger.
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Manuals
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Manuals for the data logger, communication/programming
software and each sensor should be supplied by the manufacturer.
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Communications Software
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Windows based interface communication software, such as
LoggerNet, to allow for downloading, reprogramming and real-time
monitoring of the data loggger over standard telephone line.
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SENSORS
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Temperature/RH
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HMP50C or equivalent combination temperature and
relative humidity sensor enclosed in a white radiation shield. Relative
humidity range: 0 - 100% RH, ±2% RH, operating stability ±3% RH/year.
Temperature range: +14 - 122° F.
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Soil Temperature
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Range: +15 to 120° F,
accuracy ±0.5° F with 10 foot cable.
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Solar Radiation
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LI200X or equivalent silicon pyranometer with FIXED
MULTIPLIER (11 foot lead). Accuracy: ±3% typical, ±5% minimum.
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Wind Speed
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3-cup anemometer, 1 count/revolution, AC, operating
temperature range: -50 to +120° F,
operational wind speed: 0 to 100 mph, gust survival: 130 mph, threshold:
1.5 mph, accuracy: ±1.1 mph @ 0 - 45 mph and 2.2 mph @ 45 - 100 mph.
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Wind Direction
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Operating temperature range: -50 to +120°
F, accuracy ±5° F.
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Rain Gage
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6" or greater orifice size, sensitivity: 1 tip per 0.01 inch.
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